1. Field of the Invention
The present invention relates to a semicircular plug adapted to be fitted to a cylinder head of an overhead cam shaft engine for preventing leakage of lubricating oil from the cylinder head.
2. Description of the Prior Art
In a conventional overhead cam shaft engine as shown in FIG. 1, a plurality of bearings 2 are provided in the upper portion of a cylinder head 1 for receiving a cam shaft (not shown). A semicircular recess 3 is formed in either end 1a of the cylinder head 1 in axial alignment with the bearings 2 for passing the cam shaft through the bearings 2.
In order to make the engine ready for operation, lubricating oil is supplied to the bearings 2 for lubricating the cam shaft, and a substantially semicircular plug 4 of rubber is fitted in each recess 3 to prevent leakage of the lubricating oil.
The outer periphery 4a of the semicircular plug 4 is in contact with the inner surface of the recess 3 of the cylinder head 1 as shown in FIG. 2. However, the semicircular plug 4 is not fixed with respect to the recess 3 since there is no means for securing the plug 4 to the recess 3. Therefore, when the semicircular plug 4 is pressed by a cylinder head cover (not shown) against the cylinder head 1 through a gasket 5, it tends to move out of position and develop clearances such as those shown at C.sub.1 and C.sub.2 in FIG. 2 between the top of the cylinder head 1 and the bottom of the gasket 5, through which lubricating oil leaks out.
In another conventional construction as shown in FIG. 3, the semicircular plug 4 has a projection 4b adapted to be inserted into a small hole 3a formed in the bottom of the recess 3 for preventing movement of the semicircular plug 4. In this construction, however, the semicircular plug 4 must be made of hard rubber to facilitate insertion of the projection 4b into the small hole 3a while the gasket 5 is made of soft material to prevent leakage of the lubricating oil from between the cylinder head 1 and the cylinder head cover. It is difficult for the gasket 5 to exert sufficient pressure against the semicircular plug 4 to maintain the same in a fluid-tight position, and a clearance such as that shown at C.sub.3 in FIG. 3 is created between the gasket 5 and the cyliner head 1 through which lubricating oil leaks out.